DETERMINATION OF NUCLEOSOME AND CHROMATIN STRUCTURE AND THEIR RELATIONS TO CELLULAR PHENOTYPES

Abstract

Chromatin compaction and histone acetylation are correlated with transcription. Testing these relationships requires the chromatin structure in transcriptionally active and inactive states, and by extension, the positions and connections of the nucleosomes, to be known. We genetically tagged the histone genes in the budding yeast Saccharomyces cerevisiae with GFP to try to identify nucleosomes in situ. Using cryo-electron microscopy, very few canonical nucleosomes were identified, and particles with additional GFP densities could not be identified in S. cerevisiae nucleus cryolamellae. Therefore, heterogenous non-canonical nucleosomes are the predominant form of nucleosomes. To analyse the relationships between chromatin compaction, histone deacetylation and repressed transcription, Schizosaccharomyces pombe G0 cells were used as a cellular model. When we treated G0 cells with a histone deacetylase inhibitor, almost all G0 phenotypes are unaffected and are independent of histone acetylation. Thus the relationships between chromatin compaction, histone acetylation and transcription are not direct causative relationships.